Remove default tip of 21% for pos custom tip

[myxmaster]

Description

This fixes #2698.

This pull request is categorized as a:

• New feature
• Bug fix
• Code refactor
• Configuration change
• Locales update
• Quality assurance
• Other

Checklist

• I’ve run yarn run tsc and made sure my code compiles correctly
• I’ve run yarn run lint and made sure my code didn’t contain any problematic patterns
• I’ve run yarn run prettier and made sure my code is formatted correctly
• I’ve run yarn run test and made sure all of the tests pass

Testing

If you modified or added a utility file, did you add new unit tests?

• No, I’m a fool
• Yes
• N/A

I have tested this PR on the following platforms (please specify OS version and phone model/VM):

• Android
• iOS

I have tested this PR with the following types of nodes (please specify node version and API version where appropriate):

• Embedded LND
• LND (REST)
• LND (Lightning Node Connect)
• Core Lightning (CLNRest)
• LndHub
• [DEPRECATED] Core Lightning (c-lightning-REST)
• [DEPRECATED] Core Lightning (Spark)
• [DEPRECATED] Eclair

Locales

• I’ve added new locale text that requires translations
• I’m aware that new translations should be made on the ZEUS Transfix page and not directly to this repo

Third Party Dependencies and Packages

• Contributors will need to run yarn after this PR is merged in
• 3rd party dependencies have been modified:
  • verify that package.json and yarn.lock have been properly updated
  • verify that dependencies are installed for both iOS and Android platforms

Other:

• Changes were made that require an update to the README
• Changes were made that require an update to onboarding

[kaloudis]

I think I'd prefer to add 21% as a placeholder AND fall back to 21% if the user thinks it's populated and submits with no value set

[myxmaster]

Ah right, that's the perfect solution.

[shubhamkmr04]

I think the default fees in sats should be 21% of the value, and not 2100 sats in all cases.

[myxmaster]

But using absolute amounts is the idea behind that vs. percentage...?

[shubhamkmr04]

So here the default fee is coming out as 2100 sats when we tap on it but the order value was only 396 sats ($0.37) that seems too much high for this amount.
it should be equivalent to the deafult fees in percentage, 21% of 396 sats, that is ~ 83 sats

[myxmaster]

Yeah, I know what you mean, but not sure if the absolute placeholder should be dynamic. What do you think @kaloudis ?